1. Field of the Invention
The present invention relates to an endoscope; particularly to the endoscope in which an inclined portion is provided in a distal surface of an endoscope insertion unit.
2. Description of the Related Art
Conventionally, an endoscope is widely used in the field of medicine and the like. In the endoscope, a long and thin insertion unit is inserted into a body cavity, allowing observation of organ in a body cavity and performance of various treatments with a treatment instrument inserted into an insertion channel if needed.
A bendable part is provided at a distal end of the insertion unit, and an observation direction of an observation window provided in a distal portion of an observation optical system can be changed by operating an operation unit of the endoscope to bend the bendable part.
In the conventional endoscope, for example, viewing angles of the observation optical system and observation window are 140°, and an operator observes the inside of the body cavity using an observation image with the viewing angle of 140°. When the operator observes a region outside the viewing angle, as described above, the operator bend the bendable part to observe the region outside the viewing angle.
However, for example, in observing the inside of large intestine, sometimes the desired observation image of a backside of a fold of the large intestine and the like cannot be obtained only by bending the bendable part. Therefore, in order to observe the wider range, there is provided an endoscope in which the viewing angle is widened. For example, see Japanese Patent Application Laid-Open (JP-A) No. 2001-258823.
In the endoscope proposed in JP-A No. 2001-258823, the observation optical system and observation window formed in the wide viewing angle of 180° are arranged in the insertion unit. As the observation optical system and observation window are formed in the wide viewing angle, in order to evenly illuminate throughout the inside of the body cavity, an illumination optical system provided in the insertion unit to illuminate the inside of the body cavity is arranged in an axis inclined with respect to an axial direction in which the observation optical system is provided.
Therefore, since the distal surface of the endoscope insertion unit cannot be formed in a flat shape, in the endoscope proposed in JP-A No. 2001-258823, the distal surface of the endoscope insertion unit is formed in a substantially cannonball shape.